A platform's position, velocity, and/or attitude (as well as other navigation variables) are often determined by a navigation system. The navigation variables can then be used by either a human operator or a controlling algorithm to direct the movement of the platform. The navigation variables are often determined by inertial sensors. In addition to the inertial sensors, aiding source(s), such as a global position system (GPS) receiver, may be used to supplement the data received from the inertial sensors. Inertial sensors provide measurements, such as specific force and angular velocity, as experienced by the host platform. A GPS receiver can independently provide additional platform navigation variables using signals received from GPS satellites. The navigation variables received from the inertial sensors and the aiding device(s), however, may contain errors because of, for example, open loop measurements by the inertial sensors or noise in the signals from the GPS satellites.